Time Slotted Channel Hopping (TSCH) MAC (Media Access Control) technology is a MAC technology included in an IEEE 802.15.4e MAC amendment, and is a standard technology for industrial wireless sensor networks, such as WirelessHART and ISA100.11a, that provide a high level of reliability and stability.
Devices joining a TSCH network are synchronized by time, and operate based on time, that is, in units of timeslots, and a plurality of timeslots are grouped to constitute a slotframe.
The length of a slotframe represents the number of timeslots constituting the slotframe, and the slotframes are periodically repeated during an operation time. For a single timeslot, TSCH network devices select one of a sleep operation, a transmit operation, and a receive operation, and continuously change the frequency to be used in each timeslot through a channel hopping scheme.
As described above, TSCH MAC is a multi-channel utilization technology based on Time Division Multiple Access (TDMA), and for transmission and reception, it is required to determine a channel and a timeslot (a point in time) in which a communication is to be performed.
Such an issue is referred to as TSCH link scheduling, and is an essential technique for realizing a high level of reliability and stability in TSCH MAC.
Link scheduling is performed in units of slotframes that are periodically repeated, and is achieved by allocating a link, in which a slot offset slotOffset is a relative time within the slot frame and a channel offset channelOffset is an index of an available channel list, between two devices.
The two devices are able to stably communicate with each other by using a time and a channel designated at the allocated link slotOffset and channelOffset.
However, the IEEE 802.15.4e standard, which defines the TSCH mechanism, does not define the scheduling method.
Virtual slotframe technology is a technology of combining a plurality of slotframes to constitute a virtual logical slotframe, which allows each device to use more resources without changing the length of an actual slotframe.
When the length of the slotframe, which corresponds to TSCH network settings, is changed, the changed setting generates a large amount of overhead until the changed setting is applied to the whole network, and may cause network interruption.
In the industrial field, smartfactories, manufacturing process intellectualization, and so on are of great interest, and an IIoT (Industrial Internet of Things) technology for industry is drawing attention as a new trend.
In IIoT, a sensor network device for transmitting temperature, and vibration of a device, and so on is also expected to perform various functions, such as sensing a movement of an operator and reporting the movement together. That is, a single device transmits data for various application services, and each piece of application service data is provided with a unique traffic pattern.
IEEE 802.15.4e TSCH MAC technology for IIoT provides a high reliability and stability due to Time Slotted Access and Channel Hopping characteristics.
However, in the standards, the link scheduling technology for IIoT is not clearly defined. Link scheduling technologies, which have been proposed to solve the above limitations, operate considering only a traffic pattern of a single application service or assuming only convergecast in which traffic converges from devices to a server.
In particular, link scheduling performed on a slotframe having a fixed length has difficulty in efficiently handling various traffic patterns that are generated from a plurality of application services.
For example, under the assumption that an application service A that transmits data at a cycle of 1 second and an application server B that transmits data at a cycle of 10 seconds, when the length of the slot frame is adjusted to the application service A, there is a need to allocate a link to each slotframe for the application service B, that is, to allocate an additional link to each slotframe for the data, which is transmitted every 10 seconds, and thus energy is constantly wasted.
When the length of the slot frame is adjusted to the application service B, there is a need to generate a plurality of schedules for the application service A, thereby resulting in waste of memory.
An increasing gap between traffic patterns in respective application services may lead to the worsening of the problem discussed above, and an increasing number of application services may cause a bigger problem.